Cascade electromagnetic pulse protection circuit for high frequency application

ABSTRACT

The present invention discloses a cascade EMP protection circuit, which comprises an LEMP protection circuit and a fast-response protection circuit, wherein a symmetric capacitive varactor element is cascaded to the path of signal transmission. Thereby, the present invention can protect electronic devices against LEMP or EMP released by an electronic weapon (NEMP, HEMP, or PEMP).

The present invention is a continuous-in-part application of theapplication that is entitled “CASCADE ELECTROMAGNETIC PULSE PROTECTIONCIRCUIT” (Application NO.: U.S. Ser. No. 12/134,235), which is filedpresently with the U.S. Patent & Trademark Office, and which is usedherein for reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a cascade electromagnetic pulseprotection circuit for high frequency application, which can inhibit thefast or slow overvoltage surge induced by EMP (Electromagnetic Pulse).

2. Description of the Related Art

Electromagnetic weapons may be classified into the NEMP (NuclearElectromagnetic Pulse) bomb, the HEMP (High-altitude ElectromagneticPulse) bomb, the PEMP (Portable Electromagnetic Pulse) weapon. The NEMPbomb has an affected area with a radius of hundreds of kilometers. As anuclear explosion can damage so vast an area and will cause so intensean international reaction, it is very unlikely to be directly used inthe future war. Besides, the NEMP bomb may also damage our owncommunication systems and monitoring systems. The EMP warhead carried bya long-range missile has a medium affected area with a radius of tens ofkilometers. The PEMP weapon, which is a small-size bomb carried by ahuman being or a small-size carrier, and has an affected area with aradius of less than one kilometer. In the long run, EMP bombs must beone of the weapons used in war.

The explosion of an EMP weapon will generate a pulse of a very highstrength electric field characterized in that the electric fieldstrength rises so quickly that the maximum strength is reached within 10nanoseconds, and that the electric field strength generated by the EMPweapon explosion is higher that that of an LEMP (LightningElectromagnetic Pulse) and is between 50 and 100 KV/m. The fast risingof so intense an electric field strength will induce a current as greatas thousands of amperes in an antenna or a longer cable. Because of sofast a strength rising rate, so high a voltage and so great a current,general lightning arresters are unlikely to protect electronic devicesagainst the damage caused by an EMP weapon explosion.

When an EMP rushes into a communication/information device, it mayinduce a voltage as high as from 10 to 150 kV. If there is noneprotection circuit, the front end electronic elements are unlikely totolerate such a high voltage. Currently, communication electronicdevices generally have so-called lightning arresting devices, which areusually low-speed LEMP protection elements formed of spark gap switchesor zinc oxide elements. As the LEMP protection element operates slowly,it has a long response time and a higher clamping voltage.

For current LEMP protection elements, the EMP inhibition effect isdetermined by the response time. As the spark gap switches or zinc oxideelements have a longer response time, they will not inhibit EMP untilthe surge voltage has been very high. Therefore, the current LEMPprotection elements cannot protect an electronic device against afast-rising EMP electric field.

IC (Integrated Circuit) generally has a high-speed ESD (ElectrostaticDischarge) protection element (usually TVS (Transient VoltageSuppressor), DIAC (Diode for Alternating Current), MOV (Metal OxideVaristor), etc.) at the front end. The high-speed ESD protection elementcan respond very fast and can tolerate a voltage as high as 8000V.However, the high-speed ESD protection element is not a high currenttolerant element. The electromagnetic pulse of a lightning or an EMPbomb has a greater pulse width. A longtime overvoltage induces a currenteffect and generates a large amount of heat, which will firstly burnsout the high-speed ESD protection element and then burns out theinternal structures of IC. Therefore, a high-speed ESD protectionelement can only withstand electrostatic discharge but cannot toleratehigh-energy EMP attacks.

Generally, a communication device has a lightning arresting device (LEMPprotection element), and an IC has an ESD protection element at thefront end thereof. However, even parallel connecting an LEMP protectionelement and an ESD protection element cannot yet solve theabovementioned problem. Current will firstly flow through the high-speedESD protection element, which turns on fast but cannot tolerate highcurrent, until it burns out. Then, the voltage rises again. The frontend IC maybe has burned out before the LEMP protection element starts tooperate. Besides, as all high-speed protection elements are capacitiveelements, they will result in the insertion loss ofcommunication/information devices and affect communication distance.

A Taiwan patent No. 588888, which was filed by the Inventors on Sep. 24,2002, disclosed a method to solve the above-mentioned problem, wherein arear stage ESD protection element is triggered firstly, and thepotential is established on a cascaded resistor, and then a front stagehigh-power LEMP protection element is triggered reversely. Thus, thecharge following can be drained out, and the entire system is protected.Besides, the insertion loss of input signal is also compensated.However, the conventional technology still has the problem of insertioncapacitance, which is shunt to the ground and likely to causehigh-frequency loss. In applications that the frequency is higher than 1GHz, if the small-capacitive MOV or TVS elements are adopted; thus, thecurrent draining capacity is also smaller, and the EMP impact on theperformance of electronic devices cannot be effectively reduced. Forlow-frequency applications, the conventional technology still has otherproblems to be solved. For an electric field strength higher than 300KV/m, the conventional technology still has room to improve.

SUMMARY OF THE INVENTION

The primary objective of the present invention is to provide a novelcascade EMP (Electromagnetic Pulse) protection circuit for highfrequency application to solve the abovementioned problems, wherein theinsertion loss of a fast-response protection element (or ESD element) isfurther blocked, or the structure of a fast-response protection circuitis modified, in which varactors are cascaded to signal paths (not shuntto the ground) to effectively protect electronic devices against thedamage caused by EMP.

The present invention discloses a cascade EMP protection circuit forhigh frequency application, which integrates an LEMP protection circuitwith a new type fast-response protection circuit, wherein in thefast-response protection circuit, EDS elements are self-cascaded toreduce insertion loss; alternatively, inductive elements are shunted tothe ground to save EDS elements at a higher frequency operation and forma high-pass circuit. A capacitive-reactance element is cascaded to thecircuit, wherein the capacitive-reactance element is a varactor having acapacitance varying with the input voltage. The varactor normally has ahigh symmetrical capacitance and a low impedance, which allows the RFsignal can transmit to the next device without any distortion. When anintense overvoltage EMP appears, the varactor has a low capacitance anda high impedance, which impedes surge coupling and thus protectelectronic elements from the damage of a surge pulse.

Alternatively, in the cascade EMP protection circuit disclosed by thepresent, an impedance element can be used to integrate an EMP protectioncircuit and a fast-response protection circuit, wherein thefast-response protection circuit can be self-cascaded or cascaded to acompensation element; further, the fast-response protection circuittogether with the EMP protection circuit is further cascaded by acapacitive-reactance element, which may be the varactor mentioned above.Thereby, the present invention can protect electronic devices againstEMP damage.

Below, several embodiments are described in detail to furtherdemonstrate the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematically showing a cascade EMP protectioncircuit according to a first embodiment of the present invention;

FIG. 2 and FIG. 3 are block diagrams schematically showing a cascade EMPprotection circuit according to a second embodiment of the presentinvention, wherein impedance elements are respectively arranged atdifferent positions;

FIG. 4 is a block diagram schematically showing a cascade EMP protectioncircuit according to a third embodiment of the present invention;

FIG. 5 is a block diagram schematically showing a conventional EMPprotection circuit; and

FIG. 6 is a diagram showing capacitance varying with input voltage of avaractor according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention proposes a cascade EMP protection circuit for highfrequency application, wherein a fast-response protection circuit isintegrated with an LEMP protection circuit, and a new architecture isapplied to a communication system, whereby the present invention notonly can prevent from a common lightning damage but also can protectagainst various sudden EMP attacks. Besides, insertion loss is alsoblocked. Thus, the present invention can apply to higher frequency casesand can tolerate/inhibit a higher energy surge.

Refer to FIG. 5 for a conventional EMP protection circuit, wherein afast-response protection element 43 and an LEMP protection element 41are integrated by an impedance element 42, and an insertion-losscompensation element 44 is cascaded to the fast-response protectionelement 43. A fast-response protection element generally hascapacitance; therefore, a fast-response protection element usuallycauses an insertion loss when it applies to a high-frequencycommunication device. Further, insertion loss rises with the increase offrequency. In conventional technologies, an inductive compensationelement 44 is cascaded to the fast-response element 43 to compensatefrequency. For example, in the Taiwan patent No. 588888 the Inventorsfiled on Sep. 24, 2002, the fast-response element may be a semiconductorelement (TVS or DIAC) or a zinc oxide element (MOV); therefore, thefast-response protection element itself is a capacitive element and mayfunction as a low-pass filter and can drain surge energy when a voltagesurge of thousands of volts attacks. However, the conventionaltechnologies have an inferior draining of sudden surges at a mediumfrequency because there is an inductor existing. At a higher frequency,the combination of the fast-response protection element 43 and theinductive compensation element 44 will create a retard effect and impairbroadband frequency-hopping applications.

Refer to FIG. 1 for an EMP protection circuit according to a firstembodiment of the present invention. In this embodiment, a fast-responseprotection element 13 and an LEMP protection element 11 are integratedby an impedance element 12. In medium-frequency applications, afast-response protection 14 is cascaded to the fast-response protectionelement 13 to perform compensation. As the capacitance is decreased bythe cascade of the fast-response protection elements 13 and 14, theinsertion loss is also reduced. A fuse 15 may be added to prevent froman induction event caused by that the antenna contacts a naked powercable and burns the whole circuit down.

Refer to FIG. 2 for an EMP protection circuit according to a secondembodiment of the present invention. In this embodiment, a high-passprotection inductor 24 and an LEMP protection element 21 are integratedby an impedance element 22. At high-frequency applications, thearchitecture of the original low-pass protection circuit is directlymodified into a high-pass protection circuit. The high-pass protectioninductor 24 of a high-frequency communication/information devicedirectly adopts an inductor having an inductance less than 10 nH. As thespectrum of NEMP or LEMP is less than 300 MHz, a high-frequencycommunication/information device may directly adopt a small inductor,which can prevent from insertion loss. Then, the impedance element canbe displaced to the front end, such as the impedance element 25 shown inFIG. 3. Alternatively, the impedance elements can be appropriatelydistributed on both sides of the high-pass protection inductor 24. Whena surge appears, V_(L)=L×dI/dt. The voltage generated by the inductivereactance will trigger the front-end slow-response LEMP protectionelement, and the impedance element 25 protects the rear-stage circuit.

Refer to FIG. 4 for an EMP protection circuit according to a thirdembodiment of the present invention. In this embodiment, at least onecapacitive reactance element 36 is arranged between and cascaded to asurge protection circuit 30 and a protected circuit 39. As shown in FIG.6, the capacitive reactance element 36 is a voltage control varactorhaving a symmetrical capacitance with a zero voltage as a symmetriccenter point, wherein the symmetrical capacitance varies with the inputvoltage. The voltage control varactor has a symmetrical structure suchas an MSM (Metal/Semiconductor/Metal) structure or an MISIM(Metal/Insulator/Semiconductor/Insulator/Metal) structure. The MSMstructure or the MISIM structure generates a two dimension electron gas(2DEG) therein when the voltage control varactor receives a voltage. Theenergy gap of the MSM structure or the MISIM structure has large enoughto result in the 2DEG. In a normal state, the voltage control varactoruses 2DEG to have a high symmetric capacitance and a low impedance, andsignals can reach the communication system without distortion. Forinstance, the input voltage is between 10 V and −10 V, the voltagecontrol varactor has the capacitance of 10 pF. When an intensiveovervoltage EMP occurs, the voltage control varactor uses 2DEG to have alow capacitance and a high impedence, which impends signal coupling,lest the system be damaged. For instance, the input voltage is largerthan 10 V or less than −10 V, the voltage control varactor has thecapacitance of 0.2 pF. In other words, the cascade EMP protectioncircuit of the present invention will fast trigger the protectioncircuit 30 firstly and utilizes the capacitive reactance element 36 toblock a surge; thereby, the communication system can be free from theinfluence of EMP.

Those described above are only the embodiments to exemplify the presentinvention but not to limit the scope of the present invention. Anyequivalent modification or variation according to the spirit of thepresent invention is to be also included within the scope of the claimsstated below.

1. A cascade electromagnetic pulse protection circuit for high frequencyapplication comprising: at least one voltage control varactor havingsymmetrical capacitance with a zero voltage as a symmetric center point,arranged between and cascaded to a surge protection circuit and aprotected circuit, wherein the voltage control varactor has an MSM(Metal/Semiconductor/Metal) structure or an MISIM(Metal/Insulator/Semiconductor/Insulator/Metal) structure, and whereinwhen an intensive overvoltage EMP occurs, the MSM structure or the MISIMstructure generates a two dimension electron gas (2DEG) therein wherebythe voltage control varactor has a low capacitance and a high impedence,which impends signal coupling.
 2. The cascade electromagnetic pulseprotection circuit for high frequency application according to claim 1,wherein the surge protection circuit further comprises at least onestage of LEMP (Lightning Electromagnetic Pulse) protection circuit andmore than one stage of fast-response protection circuit.
 3. The cascadeelectromagnetic pulse protection circuit for high frequency applicationaccording to claim 2, wherein an impedance element is arranged betweenand parallel to the LEMP protection circuit and the fast-responseprotection circuit.
 4. The cascade electromagnetic pulse protectioncircuit for high frequency application according to claim 2, wherein thefast-response protection circuit includes a plurality of cascaded ESD(Electrostatic Discharge) elements.
 5. The cascade electromagnetic pulseprotection circuit for high frequency application according to claim 2,wherein the fast-response protection circuit includes an ESD(Electrostatic Discharge) element and an inductive compensation elementcascaded to the ESD element.
 6. The cascade electromagnetic pulseprotection circuit for high frequency application according to claim 2,wherein the fast-response protection circuit includes an inductivecompensation element.
 7. The cascade electromagnetic pulse protectioncircuit for high frequency application according to claim 2, wherein afuse is cascaded to the LEMP protection circuit and the fast-responseprotection circuit.
 8. The cascade electromagnetic pulse protectioncircuit for high frequency application according to claim 2, wherein animpedance element is cascaded to a front end of the LEMP protectioncircuit and the fast-response protection circuit.